Recently, ink-jet recording system is begun to be applied to various fields of printing works such as photograph, various type printings and a specific printing such as that of a color filter due to easy and inexpensive image formation.
Ink-jet ink used for the ink-jet recording includes various types of ink such as an aqueous ink containing water as a principal solvent, a non-aqueous type ink containing a solvent other than water as the principal solvent, a hot-melt ink which is solid at room temperature and thermally melted for printing and an active light curable ink capable of being cured by active rays such as light, which are selected in accordance with the use.
Besides, a recording medium made from polyvinyl chloride is applied in wide using field such as a printing matter to be posted outdoor required high weatherproof capability or that to be contacted with a material body with curved surface. An ink-jet recording method is applied as a method suitable for recording on the polyvinyl chloride since in such the method plate making is not necessary and the time necessary for finishing is short so that the method suites to make small amount of diverse kinds of prints though plural methods are applicable for printing on the polyvinyl chloride medium. An ink-jet ink containing cyclohexanone is disclosed as an example of the ink-jet ink capable of recording on the recording medium made from polyvinyl chloride, cf. Patent Document 1. High anti-abrasion capability can be obtained by such the ink since cyclohexanone has high dissolving capability to polyvinyl chloride and the pigment contained in the ink comes into polyvinyl chloride. A non-aqueous ink containing N-methylpyrrolidone or an amide as the solvent is disclosed, which are weak in the odor and preferred for the working environment, cf. Patent Documents 2 and 3. Moreover a non-aqueous ink is disclosed, in which resin such as vinyl chloride-vinyl acetate copolymer or acryl resin is added for improving the strength of the image such as anti-abrasion capability, cf. Patent Documents 4 and 5.
A printing method is widely spread, in which a high color density ink and a low color density ink each having the same color are used in combination for lowering the visibility of ink dots and decreasing the granularity of image. In the case that printing method using the combination of the high color density and the low color density inks, it is found that the high color density ink and the low color density ink are difficultly ejected with sufficient stability when the driving frequency of the head is particularly high so as to cause a problem on the image formation by the high speed printing.
Patent Document 1: Japanese Translation of PCT International Application Publication No.) 2002-526631
Patent Document 2: Unexamined Japanese patent Application Publication No. (hereinafter, refereed to as JP-A) 2005-15672
Patent Document 3: JP-A 2005-60716
Patent Document 4: JP-A 2005-36199
Patent Document 5: WO 2004/007626